1. Field of the Invention
This invention relates to a hydrosilation process involving the reaction of a compound containing silicon-bonded hydrogen with a compound containing aliphatic unsaturation in the presence of ultraviolet or visible radiation, and to compositions that are useful in that process. The invention further relates to polysiloxane compositions, prepared by that process, which compositions are useful for preparing dental impressions, adhesives, release liners, and caulking materials.
2. Discussion of the Art
Numerous patents teach the use of various complexes of cobalt, rhodium, nickel, palladium, or platinum as catalysts for accelerating the thermally-activated addition reaction (hydrosilation) between a compound containing silicon-bonded hydrogen and a compound containing aliphatic unsaturation. For example, U.S. Pat. No. 4,288,345 (Ashby et al) discloses as a catalyst for hydrosilation reactions a platinum-siloxane complex. U.S. Pat. No. 3,470,225 (Knorre et al) discloses production of organic silicon compounds by addition of a compound containing silicon-bonded hydrogen to organic compounds containing at least one non-aromatic double or triple carbon-to-carbon bond using a platinum compound of the empirical formula PtX2(RCOCRxe2x80x2CORxe2x80x3)2 wherein X is halogen, R is alkyl, Rxe2x80x2 is hydrogen or alkyl, and Rxe2x80x3 is alkyl or alkoxy. The catalysts disclosed in the foregoing patents are characterized by their high catalytic activity. Other platinum complexes for accelerating the aforementioned thermally-activated addition reaction include: a platinacyclobutane complex having the formula (PtCl2xe2x80x94C3H6)2 (U.S. Pat. No. 3,159,662, Ashby); a complex of a platinous salt and an olefin (U.S. Pat. No. 3,178,464, Pierpoint); a platinum-containing complex prepared by reacting chloroplatinic acid with an alcohol, ether, aldehyde, or mixtures thereof (U.S. Pat. No. 3,220,972, Lamoreaux); a platinum compound selected from trimethylplatinum iodide and hexamethyldiplatinum (U.S. Pat. No. 3,313,773, Lamoreaux); a hydrocarbyl or halohydrocarbyl nitrile-platinum (II) halide complex (U.S. Pat. No. 3,410,886, Joy); a hexamethyl-dipyridine-diplatinum iodide (U.S. Pat. No. 3,567,755, Seyfried et al); a platinum curing catalyst obtained from the reaction of chloroplatinic acid and a ketone having up to 15 carbon atoms (U.S. Pat. No. 3,814,731, Nitzsche et al); a platinum compound having the general formula (Rxe2x80x2)PtX2 where Rxe2x80x2 is a cyclic hydrocarbon radical or substituted cyclic hydrocarbon radical having two aliphatic carbon-carbon double bonds, and X is a halogen or alkyl radical (U.S. Pat. No. 4,276,252, Kreis et al); platinum alkyne complexes (U.S. Pat. No. 4,603,215, Chandra et al.); platinum alkenylcyclohexene complexes (U.S. Pat. No. 4,699,813, Cavezzan); and a colloidal hydrosilation catalyst provided by the reaction between a silicon hydride or a siloxane hydride and a platinum (0) or platinum (II) complex (U.S. Pat. No. 4,705,765, Lewis). Although these platinum complexes and many others are useful as catalysts in processes for accelerating the thermally-activated addition reaction between the compounds containing silicon-bonded hydrogen and compounds containing aliphatic unsaturation, processes for promoting the ultraviolet or visible radiation-activated addition reaction between these compounds are much less common. Platinum complexes that can be used to initiate ultraviolet radiation-activated hydrosilation reactions have been disclosed, e.g., platinum azo complexes (U.S. Pat. No. 4,670,531, Eckberg); (xcex74-cyclooctadiene)diarylplatinum complexes (U.S. Pat. No. 4,530,879, Drahnak); and (xcex75 -cyclopentadienyl)trialkylplatinum complexes (U.S. Pat. No. 4,510,094, Drahnak). Other compositions that are curable by ultraviolet radiation include those described in U.S. Pat. Nos. 4,640,939 and 4,712,092 and in European Patent Application No. 0238033. However, these patents do not indicate that the platinum complexes disclosed therein would be useful for initiating a visible radiation-activated hydrosilation reaction. U.S. Pat. No. 4,916,169 describes hydrosilation reactions activated by visible radiation.
In one aspect, this invention provides an improved process for the actinic radiation-activated addition reaction of a compound containing silicon-bonded hydrogen with a compound containing aliphatic unsaturation, said addition being referred to as hydrosilation, the improvement comprising using, as a platinum hydrosilation catalyst, an (xcex75 -cyclopentadienyl)tri("sgr"-aliphatic)platinum complex, and, as a reaction accelerator, a free-radical photoinitiator capable of absorbing actinic radiation, i.e., light having a wavelength ranging from about 200 nm to about 800 nm. The process can also employ, as a sensitizer, a compound that absorbs actinic radiation, and that is capable of transferring energy to the aforementioned platinum complex or platinum complex/free-radical photoinitiator combination, such that the hydrosilation reaction is initiated upon exposure to actinic radiation. The process is applicable both to the synthesis of low molecular weight compounds and to the curing of high molecular weight compounds, i.e., polymers, containing unsaturated groups, e.g., 
For example, the process comprises exposing to actinic radiation, i.e., radiation having a wavelength of about 200 nm to about 800 nm, a composition capable of undergoing hydrosilation comprising: 
(c) a platinum complex catalyst having one cyclopentadienyl group that is eta-bonded to the platinum atom and three aliphatic groups that are sigma-bonded to the platinum atom, and
(d) a free-radical photoinitiator capable of absorbing actinic radiation between 200 and 800 nm, such as: 
The composition can also contain a sensitizer capable of absorbing actinic radiation having a wavelength of about 200 nm to about 800 nm, such as: 
The invention further involves novel compositions, capable of undergoing hydrosilation, containing both the aforementioned platinum complex and the aforementioned free-radical photoinitiator. The compositions can also contain the aforementioned sensitizer.
Important applications of the process and compositions of the invention include adhesives, coatings, and light curable materials for dental applications, e.g., impressions.
The main advantage of using the free-radical photoinitiator in the actinic radiation-activated addition reaction of compounds containing silicon-bonded hydrogen with compounds containing aliphatic unsaturation is the unexpectedly high acceleration of the reaction, e.g., up to about a 40% reduction in curing time.